Overly depressed freind?

what do i do? my best freind is severly depressed, he doesnt want to do anythin. he feels like all of his freinds have gone away and that he has no meanin for the world. i try to convince him otherweise but he wont listen. i hate that hes sad and such, :( and to make things worse he says hes in love with me. weve tried to date several times but everytime it ends badly.. and i keep having to reject him and i tell him i just wanna be freinds but he always goes on and on about how depressed he is. how can i make this situation better?